The present invention relates to packages for semiconductor devices, and more particularly to packages and methods of packaging semiconductor devices having plural subelements in which inoperative subelements are not connected to operative subelements.
Some semiconductor devices, particularly power devices, require a large active area to be able to carry the large currents associated with such devices. As is known, current carrying capability is a function of active area size. However, as the size of the active area increases, the yield rate (i.e., the percentage of the devices manufactured that are operative) decreases. In some high power semiconductor devices, the yield rate may be only a few percent. To increase the likelihood that the semiconductor device will be operative, the active area of the device may be divided into smaller subelements with higher yield rates, each subelement having an active area that may be selectively connected in parallel to other subelement active areas to create an active area of requisite size. While not all subelements will be operative (typically, the yield rate does not reach 100%), the number of subelements can be selected so that, on average, the number of subelements available will meet the device's current rating.
By way of example, and with reference to FIG. 1, a semiconductor device 10 requiring four units of active area to achieve its current rating may include six subelements 12, each with a yield rate of about 70% and an active area of one unit (the subelement boundaries are indicated by the dashed lines in FIG. 1). The likelihood that four or more subelements will be operative is far better than the yield rate for a device with a single active area of four units. The subelements may each include an active area 16 and a gate 18 and may be separated from the edge of the device by a termination region 14. The active areas 16 are desirably separated from each other in the silicon substrate so that inoperative subelements do not interfere with the operation of operative subelements. The distance between active areas may be reduced to save space on the device by reducing the carrier diffusion length between active areas, such as by reducing local carrier lifetimes.
The manufacture of semiconductor devices with plural subelements has presented new problems and the present invention is directed, at least in part, to solving some of those problems. For example, electrical contacts are to be made to operative subelements, but should not be made to inoperative subelements; how and when in the manufacturing process are the subelements tested; where the electrical connections should be located among operative subelements; how to make the electrical connections to the operative subelements through the package for the device?
Accordingly, it is an object of the present invention to provide a novel package for a semiconductor device with plural subelements and a novel method of packaging such a device in which operative subelements are electrically connected, while inoperative subelements are not.
It is another object of the present invention to provide a novel package for a semiconductor device with plural subelements and a novel method of packaging such a device in which the electrical connections to operative subelements are made after the device has been packaged and on top of the lid for the package.
It is still another object of the present invention to provide a novel package for a semiconductor device with plural subelements and a novel method of packaging such a device in which the active area and the gate for each subelement are contacted separately through the lid of the package for the device.
It is yet another object of the present invention to provide a novel package for a semiconductor device with plural subelements and a novel method of packaging such a device in which a contact for a subelement gate is bonded to the gate pad without decreasing the size of the active area of the subelement.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.